Summary of doctoral thesis: Improving the efficiency in using double fed induction machine in shaft generator system on shipboards

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Aims doctoral thesis: The application of doubly - fed induction machine on power-station on shipboard ensures that the two work modes working in parallel with the grid of shipboard and work independently when requiring.

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MINSTRY OF EUCATION AND TRANING HANOI UNIVESITY TRANSPORT AND COMMUNICATIONS NGUYEN TRONG THANG IMPROVING THE EFFICIENCY IN USING DOUBLE-FED INDUCTION MACHINE IN SHAFT GENERATOR SYSTEM ON SHIPBOARDS Major: Technology of Control and Automation Code: 62.52.02.16 SUMMARY OF DOCTORAL THESIS HÀ NỘI- 2014
The thesis was completed at: Hanoi University of Transport and Communications Supervisor: 1. Ass.Prof. Dr Nguyen Tien Ban 2. Ass.Prof. Dr Nguyen Thanh Hai Reviewer 1:.......................................................................................................... .............................................................................................................................. Reviewer 2:.......................................................................................................... .............................................................................................................................. Reviewer 3:.......................................................................................................... .............................................................................................................................. This thesis will be defended at Universitarian dissertation Committee at University of Transport and Communications. At ….hour…..date.…month….year. The thesis can be found at: National Library Library of University of Transport and Communications.
1 INTRODUCTION Brief The thesis studies the shaft generator system using doubly-fed induction machine on power-station on shipboards for providing solutions to improve the efficiency of energy production and saving operating costs on shipboards. The thesis consists of: 4 chapters, 113 pages, 97 references, 54 figures and graphs. Rationale While running on the sea, on the stable environment in climate and weather, the main engine propeller of shipboard often is not at full power mode, to take advantage of this excess power, the large shipboard often is designed with shaft generator working together with the diesel-generator. However, one of the complex technical issues is the stabilizing in frequency and voltage of the shaft generator when the speed of the main machine changing with the large limit, one of the effective technical solution is that using doubly-fed induction machine working in generator mode. The advantages of DFIG in the power generation systems is that the stator is connected directly to the grid and the rotor is connected to the grid through the control circuit. Because the control circuit is in the rotor, the power of the control circuit is much less than the power fed in to the grid, and the generating power is fed into the grid directly. Because of the above reasons, the author chose title “Improving the efficiency in using doubly-fed induction machine in shaft generation system on shipboards” to perform the thesis. Aims The application of doubly-fed induction machine on power-station on shipboard ensures that the two work modes: 1.Working in parallel with the grid of shipboard; 2.Work independently when requiring. In the thesis, the authors delve into the ability to work in parallel with the shipboard grid by proposing a new structure with a simple control system, which is high quality, stable imitation of the grid voltage. In the thesis, the author also presents the method of caculating optimum angular speed of DFIG rotor so that the conversion efficiency from mechanical engergy into electrical energy in shaft generators on shipboards is maximal. Hence, the transmission system between the main engine and DFIG rotor with the reasonable ratio of transmission is designed in order that the
2 consumption of fuel for producing one electrical unit in shaft generators used DFIG is minimum. The subject and scope of research The subject of thesis include of: - The doubly-fed induction machine. - The control system structure of the doubly-fed induction machine in shaft generator. The scope of thesis: Researching the shaft generator working in parallel with the grid on shipboard. Results - The results of scientific is that proposing the new control structure of the doubly-fed induction machine in shaft generator on shipboards, improving the efficiency in using doubly-fed induction machine in shaft generation system on shipboards. - The results of practical is that reducing the consumption of fuel for producing one electrical unit in shaft generators used DFIG, which plays an important role in saving operating costs on shipboards. ***************** CHAPER 1: OVERVIEW OF SHAFT GENERATOR SYSTEM ON SHIPBOARD USING DOUBLE FED INDUCTION MACHINE AND RELATED RESEARCHS 1.1 Overview of shaft generator on shipboard Figure 1.1: The system structure of shaft generator using doubly-fed induction machine The symbols in Figure 1.1 are as follows: 1.Propeller; 2.Shaft generator; 3.Gearbox; 4. Main machine; 5.The controller of shaft generator power; 6.The power distribution cabinet; 7.The diesel-generator. 1.2 The shaft generation systems in practices
3 1.2.1 The ways to layout for shaft generator to receive the energy from main machine 1.2.2 The electrical structure of of shaft generator 1.3 The general diagram of the control system of shaft generator using doubly-fed induction machine The control circuit has two main parts: The grid-side converter control system and the rotor-side converter control system, two parts are connected together through the DC circuit. Figure 1.11: The tructure of control system of doubly-fed induction machine in shaft generator 1.4 Summary of the research results and the applications of DFIG in generation systems Currently, the generator system used DFIG occupies close to 50% of the wind energy market [48], include of 93 models of various manufacturers around the world [71]. There are many national and international researchs on DFIG control, the control structure typicals are as following. 1.4.1 The scherbius static control structure The first two systems using the structure Scherbius are: 1.The static Kramer structure [23][46][85][91]; 2.The cycloconverter connected between the stator and the rotor. 1.4.2 Space vector control Some of national and international researches on DFIG control base on space vector for the shaft generator are [1][2][6][27], In addition, there are many related researches or is the similar researches, which are researches on the generator wind used DFIG.
4 1.4.3 The direct torque control technique (DTC) The advantage this method is the good performance of the energy conversion [14][15][18][22][73][74][90]. ABB has developed the power converter to control DFIG using this technique [92]. 1.4.4 The direct power control technique (DPC) The structure of DPC follows the same philosophy of DTC, but it also looks at the effect of the stator and rotor ﬂuxes upon the stator active and reactive power into the grid [13][79][85][90]. 1.4.5 The sensorless control structure of DFIG There are some methods of DFIG sensorless control are as below: - The model reference adaptive system observers [16][25][28][30][34][40][61][66][83]. - The open-loop sensorless methods[17] [20] [32][41][57]. - The other sensorless control structure of DFIG. 1.4.6 Brushless- Doubly–Fed Induction Generator (BDFIG) The disadvantages of the generator system using DFIG are slip rings and carbon brushes. A structure is proposed to overcome this disadvantage is the combination of DFIG called Brushless- Doubly–Fed Induction Generator, this system has been feasible applied in practice [19][21][78][89][96]. 1.5 The problem and proposing solution, objective of thesis The thesis proposes the new control structure of the doubly-fed induction machine in shaft generator on shipboards basing on the rotor similar signal method. The control structure of the doubly-fed induction machine will be simplified. Moreover, applying this method will improve the quality of the shaft generator on shipboards The thesis also researches and calculates the range of angular speed of the doubly-fed induction machine so that the conversion efficiency from mechanical energy into electrical energy in shaft generators on shipboards is maximal. Hence, the transmission system between the main engine and the rotor of the doubly-fed induction machine with the reasonable ratio of transmission is designed in order that the consumption of fuel for producing electrical power in shaft generators is minimal 1.6 The content and methodology of the thesis The content of the thesis researches on the shaft generator systems using DFIG on shipboard. Then, proposing the solution to improve the efficiency in using doubly-fed induction machine in shaft generation system on shipboards.
5 The research methodology of the thesis is based on the characteristics, properties and mathematical model of DFIG, the characteristics of the shaft generator on ships for analysing, and proving the new proposed model of DFIG control with high performance. And verifing the results obtained by simulation in Matlab software. Comments and conclusions of Chapter 1 ***************** CHAPER 2: PROPOSING THE STRUCTURE OF SHAFT GENERATOR USING DFIG ON THE BASIS OF SIMILAR SIGNALS FORM ROTOR 2.1 The equations of DFIG 2.2 The structure of cascade DFIG system applied in power generation 2.2.1 The structure of generator using brushless DFIG The structure and the operation principle of the cascade DFIG: Hình 2.3: The structure of cascade DFIG with converter on the stator Today, this system has built on the singer frame and do not need brushes. Hình 2.4: The Brushless-Doubly-Fed Induction Generator -BDFIG [97] 2.2.2 The structure of generator using DFIG on the basis of similar signals from rotor
6 Hình 2.7: The structure of generator using DFIG on the basis of similar signals from rotor The system includes of: two doubly-fed induction machine DFIG1, DFIG2, the stage of signal processing and the current control circuit. The signal in all the stages of this system are similar to the voltage signals in the rotor DFIG1. Therefore, this method is also called the control method on the basis of similar signal from rotor. 2.3 The mathematical model of shaft generator system using DFIG on the basis of similar signal from rotor 2.3.1 The structure and the principle of operation Hình 2.8: The shaft generator system using DFIG on the basis of similar signal from rotor The system includes of:  The main machine (ME) with the shaft is connected to the shafts of DFIG2 and DFIG1.  DFIG1: is a small capacity doubly-fed induction machine with its function is creating the similar voltage signal in the rotor.
7  Similarity and isolation stage: is a signal amplifier circuit using operational amplifier with high-input resistance so that the rotor of DFIG1 is in the open circuit mode  Current control circuit: to create the currents fed into the rotor of DFIG. At this stage, the value of the output current is equal to the value of the input voltage signal.  DFIG2: is the doubly-fed induction generator, and its function is creating the voltages and the currents which are fed into the grid. Shafts of DFIG1 and DFIG2 are tightly connected to each other to make the angles of their stators and rotors equal. Because there are two doubly-fed induction machines in the system so the parameters are presented as: 1Y for DFIG1, 2Y for DFIG2. 2.3.2 The mathematical model of DFIG1 and DFIG2 On axis oriented along the grid-voltage vector position, the equations of voltage vector and the stator flux vector of DFIG1 are presented as below:  1 f 1 1 f d (1 f ) 1 f s  u s  Rs . i s   j. s .  s  dt  1 f ( 2 . 65 .a , b , c , d )  1 u f 1R .1 i f  d (  r )  j. .1 f  r r r dt r r 1 f 1 f 1 f 1 1   s  i s . Ls  i r . Lm 1 f 1 f   r  i s .1 Lm 1 i rf .1 Lr  Because of the hight resistance of the similarity and isolation stage, the rotor of DFIG1 works in the open circuit mode, so 1 i rf  0 ,the flux vector of stator and rotor of DFIG1 are as below:  1 f  1 i sf .1 L s  s ( 2 .66 .a , b ) 1 f 1 f 1   r  i s . Lm  The equations of the stator and rotor voltage of DFIG1 are as below:  1 f 1 1 f 1 d (1 i sf ) 1 f  u s  R s . i s  Ls .  j. s .1 Ls . i s  dt ( 2 .67 .a , b )  1 f  1 u f 1L d ( i s )  j. .1 L .1 i f   r m dt r m s 2.3.3 The system model of DFIG2 before connecting stator of DFIG2 to the grid When the stator of DFIG2 is not connected to the grid, 2 i sf  0 , the flux vector of stator and rotor of DFIG2 are as below:
8  2 f  2 i rf 0 .2 Lm  s ( 2 . 69 .a , b ) 2 f 2 f 2   r  i r 0 . Lr  The equations of the stator and rotor voltage of DFIG2 are as below: 2 f 2 f 2 d ( ir0 ) 2 f  u s  Lm .  j. s .2 Lm . i r 0  dt ( 2 . 70 .a , b )  2 f  2 u f  2 R .2 i f  2L . d ( i r 0 )  j. .2 L .2 i f   r r r0 r dt r r r0 The output voltage of the DFIG1 rotor (in equation 2.65b) goes through to the similarity and isolation stage, then generates the voltage u ss is as below: f 1 f f 1 f d( i s ) 1 f u ss  Gss . u r  Gss .(1Lm .  j.r .1Lm . i s ) ( 2 . 71 ) dt In the voltage modulation of DFIG2 rotor, offset component 2 R r .2 i rf 0 , Therefore the votage into the rotor of DFIG2: 1 f 2 f 1 f 2 f 2 f d( i s ) 1 f ur  u ss 2Rr . i r0 2Rr . i r0  Gss (1Lm  j.r .1Lm. i s ) ( 2 . 72 ) dt Compare with the rotor voltage equation of DFIG2 in equation (2.70b): 1 f 2 f 2 2 f d( i s ) 1 f 2 f d ( i r0 ) 2 f Rr . i r 0  Gss (1Lm .  j.r .1 Lm . i s )  2Rr . i r 0  2Lr .  j.r .2 Lr . i r 0 dt dt => 2 i rf0  K 12 .1 i sf (với K 12  G ss .1 L m / 2 L r ) ( 2 . 73 ) Replace 2 i rf0  K 12 .1 i sf into equation (2.70a), we receive the stator voltage of DFIG2: 1 f 2 d( is ) 1 f u fs  K12 (2Lm .  j.s .2 Lm . i s ) ( 2 . 74 ) dt Research the equation (2.65a), which is the equation of stator voltage of 1 f DFIG1: 1 u fs 1Rs .1 i sf 1Ls . d ( i s )  j. s .1 Ls .1 i sf ( 2 .65 .a ) dt We have the remarks as follows:  u s is the grid voltage. 1 f 1 f  The phase difference between 1 d( is ) 1 f and the f u sl 1Ls .  j. s .1 Ls . i s dt 1 f component of grid voltage 1 u fs 1Rs .1 i sf 1Ls . d ( i s )  j.s .1 Ls .1 i sf is const. dt  2 u / u  K12. Lm / Ls  const, so that the phase of f 1 f s sl 2 1 2 u f s are equal to those of 1 u sl . f We have the results as follows:
9  The phase difference between the output voltage of DFIG2 and the grid voltage is very small and const.  Because the phase difference is const, so it can be compensated by rotating the shaft between DFIM and DFIG. Or, the phase difference is very small it can be neglected.  We can adjust the amplitude of the output voltage of the DFIG to be equal to the amplitude of the grid voltage by adjusting Gss. The components of the current in the rotor of the DFIG: The component of the d axis current DFIG2 2ird 0 is created by adding phase to 2 f i r0 an angles π/2. The component of the q axis current DFIG2 2irq0 is created by reverse-phase 2 i rf 0 . 2.3.4 The system model of DFIG2 after connecting stator of DFIG2 to the grid On axis oriented along the grid-voltage vector, the DFIG feeds the grid with the current 2 i sf , the rotor current vector of the DFIG has to be evaluated as follows: 2 i rf  2 i rf 0  2 i rt , f The equations of the current components along the d and q axis:  2isd  (2Lm / 2Ls )2irtd  ( 2 .85 .a , b ) 2 2 2 2  isq  ( Lm / Lm ) irtq  Controlling the power: The active and the reactive power of the stator of the DFIG are as: 2 2   P  (3 / 2). u sd . isd ( 2 .89 .a , b )  2 2 Q  (3 / 2). u sd . isq  Replace 2 isd (2.85a) and 2isq (2.85b) into equations (2.89.a,b): 2 2 2 2  P  (3 / 2). u sd . irtd .( Lm / Ls ) ( 2 .90 .a , b )  2 2 2 2 Q  (3 / 2). u sd . irtq .( Lm / Ls )  As can be seen in section 2.3.3:  2irtd  GP .2 ird 0  ( 2 .91 .a , b ) 2 2  irtq  GQ . irq 0  (Where 2 irq 0 is created as: 2 irq 0  2 i rf0 ; and 2 ird 0 is created by rotating the vector 2 i rf0 an angles π/2). Replace 2irtd and 2irtq to calculate the P, Q:
10 P  (3 / 2).(GP .2 ird 0 ).2 usd .(2Lm / 2Ls )  GP . X   2 2 2 2 Q  (3 / 2).(GQ . irq0 ). usd .( Lm / Ls )  GQ .Y  ( 2 .92 .a , b ) Where X, Y are the steady components because on axis oriented along the grid-voltage vector position, 2usd , 2ird 0 , 2irq0 are steady. Therefore, to adjust the active power P of the DFIG fed into the grid, we only need to adjust GP. To adjust the reactive power Q of the DFIG fed into the grid we only need to adjust GQ . Finally, the block diagram of the system model connected to the grid is presented in fig 2.13: Figure 2.13: The system tructure of the shaft generator using doubly-fed induction machines on the basis of similar signals from rotor after connecting to the grid 2.3.5 The advantages of the shaft generator system using doubly-fed induction machines on the basis of similar signals from rotor After adjusting Gss at the similarity and isolation stage, the phase, frequency and amplitude of the output voltage of the DFIG always equal to those of the grid voltage even when the grid voltage and the rotor speed of the DFIG change. Base on this method, the generation system has a simple control structure but operates effectively. Which ensures to decouple the active and reactive power supplied to the grid by using two separate parameters Gp and Gq. 2.4 Determining the the gear ratio of the shaft generator 2.4.1 The structure and the function of gearbox in shaft generator 2.4.2 The energys flowing through the generators
11 Figure 2.16: The structure of the energys flowing through generators 2.4.3 The component of power through generator 2.4.3.1 The power of the main engine 3M2   ( 2 .100 ) Pc  M c .    sr 2 L ird irq  M 0      s   2.4.3.2 The stator power of DFIG 3 M 3 2 ( 2 .102 ) P 1 (s M sr irq )( sr ird )  s ( M sr / Ls )ird irq 2 Ls 2 2.4.3.3 The rotor power of DFIG 2 2 P2   r P1 /  s  (3 / 2 ) R r (ird  irq ) ( 2 .107 ) The angular frequency  r 0 of rotor current for P2=0 is: 2 2 3   Ls  2  u sd   Rr    u sd   X    2   M sr   r0  s    sr   (where X sr   s .M sr ). P1 So the angular speed of the rotor is: 2 2  3   Ls  2  u sd    Rr    isd      2   M sr  X   ( 2 .110 )  0   s 1     sr    P1        2.4.4 The performance of the convertion mechanical energy into electrical energy 2.4.4.1 The case of    0 The performance of the convertion mechanical energy into electrical energy is as below:
12 P  P2 H bt H  1  Pc 2 M 2  2 2 ( 3 / 2 ) s ( M sr / L s ) i rd i rq  (3 / 2 )(  s   ) i rd i rq  sr  H bt  ( 3 / 2 ) R r ( i rd  i rq ) H bt  L   s  ( 2 .112 ) 2  3  M sr      i i  M 0   2  L  rd rq    s   The derivative of performance H is as below: 2 2 ' P1 (1  H bt )  (3 / 2) R r (i rd  i rq ) H bt ( 2 .113 ) H  P    1  M 0  2    s  H  0, '   0 , H=max the angular speed of the rotor is    0 . Combine 2 cases, we have the results: H=max the angular speed of the rotor is:
13 2 2  3  L  2  u sd    R  s  isd      2 r   M sr  X   ( 2 .117 )  0   s 1     sr    P1        Comments and conclusions of Chapter 2 ***************** CHAPER 3: SURVEYING BY SIMULATION TO VERIFY THE CORRECTNESS OF THE SYSTEM PROPOSED 3.1 Introduction 3.2 The function stages of the system Figure 3.1: The system tructure of the shaft generator using doubly-fed induction machines on the basis of similar signals from rotor
14 3.3 Building a the model of the system Figure 3.2: The simulation model of the system 3.4 The way to adjust and operate the system 3.4.1 Adjusting the system before connecting the stator of DFIG2 to the grid Setup the coefficients Gp and Gq are zero, the phase and frequency of the DFIG2 voltage alway equal to those of the grid voltage, so we only need to adjust the amplitude of the DFIG voltage by adjusting Gss. 3.4.2 Operating of the system after connecting the stator of DFIG2 to the grid To adjust the active power P of the DFIG fed into the grid, we only need to adjust GP. To adjust the reactive power Q of the DFIG fed into the grid we only need to adjust GQ. 3.5 The simulation the characteristics of the stages in the system 3.5.1 The simulations before connecting the stator of DFIG2 to the grid
15 The process of adjusting GSS: time(s) Figure 3.7: The process of adjusting Gss When the rotor speed (ɷ) changes changes: time(s) Figure 3.8: when the rotor speed ( changes (ɷ)
16 time(s) Figure 3.9: The grid voltage is reduced before connecting he the stator of DFIG2 to the grid Before connecting the stator of DFIG2 to the grid, after adjusting Gss, the efore adjusting phase, amplitude and frequency of the output voltage of the DFIG2 always equal to those of the grid voltage, even when the rotor speed of the DFIG and the grid voltage changes. 3.5.2 The simulation after connecting the stator of DFIG2 to the g simulations grid Adjust the active power P and reactive power Q through Gp and Gq q separately separately: time(s) Figure 3.10: Responding when GP and GQ changing hen
17 When the rotor speed chang changing: Setup GP và GQ are const (GP=10, GQ=0). G time(s) Figure 3.11: Responding when the rotor speed change hen rotor Responding when the grid voltage change change: time(s) Figure 3.12: Responding when the grid voltage change hen
18 Comments and conclusions of Chapter 3 ***************** CHAPER 4: ESTABLISHING THE CONTROL SYSTEMS FOR DOUBLE FED INDUCTION MACHINE IN SHAFT GENERATOR SYSTME ON SHIPBOARDS 4.1 Introduction 4.2 Identifying the structure of control object Figure 4.2: The block diagram of the control object 4.3 Designing controllers 4.3.1 Overview of fuzzy control system 4.3.2 Designing of PID controller tuning fuzzy to control subjects a) b) Figure 4.5: The system control of the components power Considering the control channel of the active power P: The fuzzy tuner:  The linguistic levels of the error and error derivational (e and ė) are assigned as: negative big (NB), negative (N), zero (Z), positive (P), and positive big (PB), with the range of each inputs are [-1 1] (pu).  The linguistic levels of the outputs (KP, KI and KD) are assigned as: very small (VS), small (S), zero (Z), big (B), and very big (VB), with the range of each outputs are [0 1] (pu).  Those linguistics term by triangular-shape membership functions.  The rule base is build by an expert’s experience, the rule base for KP, KI, KD fuzzy tuner are presented in table 4.2.  Finally the outputs can be obtained using a max-min fuzzy inference and the crisp output is calculated by centre of area method.